Attitude control — III

THE AGE OF SATELLITES is here. With it has come some interesting attitude control problems. For many uses, it is desirable to have a satellite oriented in a unique attitude with respect to the earth. If such a unique stable attitude exists, the attitude-control problem is reduced to a damping problem. Two methods have been proposed to obtain a stable attitude. These methods use (1) the gradient in the earth's gravitational field, and (2) aerodynamic torques. Each method requires that the vehicle have certain properties. In gravity gradient stabilization, it is necessary that the vehicle have a single axis about which the moment of inertia is a minimum. In the stabilized position, this axis becomes aligned to the vertical.
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In aerodynamic stabilization, it is necessary that the center of pressure lie behind the center of mass in the direction of the vehicle's velocity.